Electrical musical instrument



Nov. 5, 1940. e. w. DEMUTH ELECTRICAL MUSICAL INSTRUMENT Filed March 31, 1959 w w u WW m M m I a m m 1 N G a E W m m p C m z 7 v 2 ia; 7 MW W 3 Gdla'n WDemuth u (Ittorneg Patented Nov. '5, 1940 UNITED STATES PATENT OFFICE I 2,220,109 ELECTRICAL MUsrcAL msrauMENr Galan W. Demuth, Westville, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application March 31, 1939,: Serial No. 265,277

musical instruments wherein the vibrations of strings or other vibrating members are electrical- 8 1y picked up either electromagnetically or electrostatically and transmitted preferably through an electronic amplifier to an appropriate sound The invention is particularly ap- 1 reproducer. plicable to pianos having electromagnetic pick- 10 ups adjacent to the strings and wherein separate controls of the bass and treble volumes are required. In such devices it *has heretofore been customary to group the treble pickups together in one circuit and to group the bass pickups to- I; gether in another circuit, each of these circuits having appropriate tone control or possibly even an individual amplifier.

In such an arrangement if the volume of output from the treble portion of the instrument, for example, is made very low and the output from the bass portion is made very high, then as the player reaches the cross-over there is a sudden change in volume between two adjacent notes instead of a gradual change from the one portion of the keyboard to the other. other hand, an amplifier is used having a characteristic which can be shifted one way or another so as to selectively accentuate the treble or the bass, a corresponding shift in tone quality results. For example, if the bass is accentuated and the volume in the treble is decreased, then the corresponding overtones of the bass notes are decreased in amplitude.

In apparatus according to the present invention, separate groups of pickups in the treble and in the bass are used each with its separate volume control to avoid distortion; but the notes at the adjacent ends of the treble and bass scales are provided'with divided pickups, a portion of the turns otthe pickup coil being connected to the treble circuit and a portion of the turns being connected to .the bass circuit. The number of turns in each pickup which are connected to the one output circuit may be progressively decreased as the notes are farther away from that circuit, and the turns connected to the other .circult correspondingly increased. By the use of this arrangement, a sharp transmission point is avoided and a gradual progression from one portion of the keyboard to another is accomplished independently of the relative volumes in the different portions of the keyboard and without any noticeable distortion.

It will be apparent that the application of the invention is not limited to a transition between If, on thethe treble and bass portions of a piano keyboard but that the keyboard may be divided if desired into three or more parts, each with its appropriate volume control and with an appropriate group of transition pickups blendingeach 5 of the sections into the next; as, for example, the groups may be divided into the treble, the intermediate, and the bass, or one group of pickups may be applied to the upper range of the piano where three string unisons are used for each note, another group of pickups to the middie and upper boss ranges where two string unisons are used, and a third group of pickups to the lower bass range where single strings are used with appropriate transition pickups at each changeover point.

The invention, of course, is not limited to pianos or stringed instruments, but may be applied to different types of apparatus where a plurality of pickups or impulse sources are used to cover an extended range of frequenciesas, for example, in electric organs and in instruments, using tuning forks, vibrating bars or other equivalent generators of the sound frequencies.

Likewise the invention may be applied to electrostatic, piezo electric or other types of pickup elements by using either sub-divided pickups as in the case of electromagnetic pickups or by using voltage or current dividers across the individual pickup units to direct appropriate portions of the output to the higher and lower frequency output circuits.

One object of the invention is to provide an improved type of pickup system for electric musical instruments.

Another object of the invention is to provide an electric musical instrument capable of producing difierent volume levels in diiferenti frequency v ranges without distortion.

Another object of the invention is to provide an apparatus having a smooth transition from one volume and frequency range to a different volume and frequency range.

Another object of the invention is to provide an electric musical instrument having a plurality of independently controllable output circuits.

Another object of the invention is to provide an electric musical instrument having a volume characteristic which can be varied according to frequency without producing distortion.

Other and incidental objects of my invention will be apparent to those skilled in the art from a reading of the following specification and an pection of the accompanying drawing, in which 4 Figure 1 is a schematic diagram of my improved pickup circuit from the vibrating members to the amplifier input circuit, and

, gure 2 shows the response characteristic of the circuit plotted against frequency. I Referring first to Fig. 1, the vibratable elements are indicated at l0 and in the form of the invention illustrated these may be vibratable strings, reeds, forks or the like, the higher frequency elements being toward the top of the sheet and the lower frequency elements being toward the bottom. ,The number of elements, of course, may correspond to any desired frequency range. For example, in a piano the number of notes'would ordinarily be 88, with a corresponding number of pickup locations and with a correspondingly greater number of strings. The high frequency pickups are generally indicated at l I and 12, these pickups being in proper cooperative relation with the high frequency vibrators. The low frequency pickups are'in'dicated at I3 and M. The high frequency pickups direct their output to the transformer 2'! and the output control potentiometer 28, while the low frequency pickups direct their output to the transformer 29 and the potentiometer 30. Between these two groups of pickups are provided the transition pickups schematically indicated at l5, l6, l1 and I8. These, of course, may be considerably greater in number, being preferably spread over a range of the order of an octave. The transition pickups 15 and I6 toward the treble end of the scale are provided with coils having a relatively large number of turns l9 and 20 which are connected to the trble output transformer 21 and these pickups l5 and I6" are also provided with coils 2| and 22 having a smaller number of turns connected to the bass output transformer 29. The pickups H and 18 toward the bass end of the transition are provided with coils 23 and 24 having the larger number of turns connected to the bass output transformer 29, while the coils I! and I8 having the smaller number of turns are connected to the treble output transformer 21. It will be apparent that the major portion of the output from the pickups l5 and I5 is delivered through the coils l9 and 20 to the treble output circuit, while the smaller portion of the output is directed through coils 2i and 22 to the bass output circuit and its corresponding volume control. If therefore the treble volume control 28 is turned to a very low level, the output from these two pickups will be greatly reduced but a considerable por tion thereof will be picked up by the coils 2| and 22 and may be reproduced at a fairly high level, through the bass control 30. It will also be apparent that in the case of the pickups I? and 18 a lowering of the volume from the potentiometer 28 will decrease the outputs from these pickups through the coils I? and I8 but in a much less degree than with the pickups i5 and I6 and, therefore, as the notes sounded go progressively from the treble into the bass, the portion of the output of the vibrators will increase until the full output is reached from the pickups l3 and M.

The frequency characteristics of such a circuit over the range, for example, from 27 cycles to 4.000 cycles is indicated in Fig. 2 showing that at the lower end of the scale at 27 cycles, the bass' circuit provides the entire output and at the higher frequency of 4000 cycles, the treble circuit provides the entire output. Over the transition range, however, when the output from the .bass circuit is decreased a certain amount the oz'tput of that same note through the treble circuit is increased by a corresponding amount, equal portions being directed through the bass and treble circuits at the middle of the transition. pointed out above, the number of-turns fed into each circuit through the pickups over the transition frequencies is varied in accordance with the number of notes over which the transition is spread and the ratio of turns in each pickup feeding to the respective circuits is preferably the corresponding fraction of the totalnumber of turns.

In the case of capacity pickups, the relative areas of the capacitors are preferably varied in the same proportion, and in the case of piezoelectric or similar pickups where size is not so readily variable voltage dividers may be connected across each pickup in order to apportion the out.- put correspondingly between the 'two output circuits. i

It is well known to those skilled in the art that overa portion of their range, pianos customarily have three strings for-each note, over another portion of the range two strings for each note, and in the extreme bass, only one string for each note, and each of the groups of strings, although ,single note, according to the harmonics desired,

but the resultant frequencies may then be multiplied and selected for the individual notes to be produced, harmonics of the original notes to be selected may be reproduced, or several harmonics may be selected for reproduction. In the case of such an electric organ instead of applying my selective pickups to the primary oscillation producers, I may apply them in the form of corresponding transformer windings to the secondary oscillation producers i. e. to the output of the cir-- cuits which detern'iine the particular noteto be produced when any particular key is pressed, independently of which of the primary oscillators or sound producers the particular sound originates in. In the following claims, the reference to pickups corresponding with the number of note producing means is to be construed in view of the foregoing explanation as indicating a correspondence to the keyboard and as refeiling to "one or more strings in the case of instruments like the piano or with the fractional outputs from the oscillators, tone wheels c? the like.in the case of an electric organ.

Having now described my invention, I claim: 1 An apparatus of the class described including impulse sources of sequential frequencies, a plurality of output circuits each having a volume control therein, a plurality of pickups corresponding in number with said impulse sources, the pickups in one portion of the frequency range being connected to one of said output circuits, the

pickups in another vicinal portion of the fre-' producing means, the pickups in one portion of the frequency range being connected to one of said output circuits, the pickups in another vicinal portion of the frequency range being connected to another of said output circuits and the pickups in the frequency range between the said two portions being connected to both of said output circuits in proportion to their relative frequencies.

3. In apparatus of the class described having a plurality oi means for producing notes of sequentialirequencies, a plurality of output circuits each having a volume control therein, a plurality of inductive pickups corresponding in number with the note producing means, the pickups in one portion otthe frequency range being con-v nected to one of said output circuits, the pickups in another vicinal portion of the frequency range being connected to another of said output circuits, and the pickups in the irequency range between the said two portions each having a portion of its inductance connected to one and another portion of its inductance connected to the other 01' said output circuits;

4. The combination of a plurality of means for producing oscillations oi diflerent irequencies, a plurality of output circuits having volume controls therein, a plurality oi pickups corresponding in number with the oscillation producing means, the said pickups in one portion of the frequency range beingconnected to one of said output circuits, the pickups in another portion of the frequency range being connected to the other of said output circuits and the pickups in the frequency range between the said two portions being connected to both of said output circuits.

GALAN W. DEMUI'H. 

